Foldable wheelchair and link configuration for foldable wheelchair

ABSTRACT

A link configuration for a wheelchair having laterally spaced side frames comprises a plurality of links extending between the wheelchair side frames. Each link has opposing ends. One of the ends of each link is pivotally coupled to one of the side frames. The other end of each link is pivotally coupled to the other side frame. Each link has a hinge to permit the links to fold. The links are foldable in non-parallel planes relative to one another. An interference member coupled to the hinge of one of the links is engageable with the hinge of the other link upon unfolding the links to couple the links together.

BACKGROUND

Foldable wheelchairs generally comprise cross-tubes pivotally mountedbetween the wheelchair side frames. The cross-tubes generally form ascissors-like arrangement that requires the side frames to be arrangedparallel to one another. This parallel arrangement is usually not wellsuited for withstanding lateral deflection resulting from lateralloading. Moreover, the physical requirements of the cross-tubes affectthe dimensions within which the wheelchair may be folded.

Foldable panels or struts may be used in the place of cross-tubes.Foldable panels and struts may be used in combination with one another.For example, a foldable seat panel is commonly used in combination witha foldable strut. Foldable panels and struts generally employ a varietyof centering and locking configurations used to lock the panels andstruts in an unfolded position to prevent the panels and struts frominadvertently folding. Centering and locking configurations are oftencumbersome and typically require the performance of a series of steps tobe implemented.

A simple, lightweight and dependable low-cost link configuration capableof withstanding lateral deflection is needed.

SUMMARY

The invention is directed to a link configuration that satisfies theforegoing as well as other needs. A link configuration for a wheelchairhaving laterally spaced side frames comprises a plurality of linksextending between the wheelchair side frames. Each link has opposingends. One of the ends of each link is pivotally coupled to one of theside frames. The other end of each link is pivotally coupled to theother side frame. Each link has a hinge to permit the links to fold. Thelinks are foldable in non-parallel planes relative to one another. Aninterference member coupled to the hinge of one of the links isengageable with the hinge of the other link upon unfolding the links tocouple the links together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial side elevational view and partial schematicrepresentation of a wheelchair having a link configuration according tothe present invention.

FIG. 2 is a partial cross-sectional, partial elevational view of a linkaccording to the invention and a support tube for use with the link,with a saddle washer for use with the support tube shown in hidden line.

FIG. 3 is a partial front elevational view of the link shown in-part inFIG. 2, with inner walls of a strut tube and features of an end cap ofthe link at least partially shown in hidden line.

FIG. 4 is a partial, partially exploded bottom plan view of the linkshown in-part in FIGS. 2 and 3, with features of the end cap of the linkshown in hidden line.

FIG. 5 is a partial side elevational view of the link shown in FIGS. 2through 4, with features of the end cap and a centering and lockingassembly of the link shown in hidden line.

FIG. 6 is a front perspective view of a swivel bracket forming a part ofthe centering and locking assembly shown in FIG. 5.

FIG. 7 is a partial, partially exploded side elevational view of anotherlink according to the invention.

FIG. 8 is a partially exploded top plan view of the link shown in FIG.7, a partial top plan view of opposing wheelchair seat tubes, withcoaligning strut hinge holes shown in hidden line.

FIG. 9 is a partial bottom plan view of the link and the opposingwheelchair seat tubes shown in FIG. 7, with a guide of the link engaginga portion of the seat tubes.

FIG. 10 is a diagrammatic representation of the links shown at least inpart in FIGS. 3 through 9.

FIG. 11 is a partial front elevational view of the links shown in FIG.10 with the links being centered and locked by the centering and lockingassembly.

FIG. 12 is a partial side elevational view of the centering and lockingassembly shown in FIG. 11.

FIG. 13 is a side elevational view of a wheelchair having an alternativelink configuration, and a schematic representation of a rear wheel and afront caster.

FIG. 14 is a partial, partially cutaway front elevational view of anupper portion of the wheelchair and the alternative link configurationshown in FIG. 13.

FIG. 15 is a partial, partially cutaway front elevational view of alower portion of the wheelchair and the alternative link configurationshown in FIG. 13.

DESCRIPTION

Referring now to the drawings, there is illustrated in FIG. 1 awheelchair 110. The wheelchair 110 comprises a pair of longitudinallyextending, laterally spaced side frames 112. To simplify thedescription, only one of the side frames 112 is shown. The side frames112 are supported on a supporting surface S by a pair of opposing frontwheels or casters 114 and a pair of opposing rear drive wheels 116. Onlyone of the front casters 114 and rear wheels 116 is schematicallyrepresented. The side frames 112 support a laterally extending seatpanel 118 and a seat back, generally indicated at 120. The seat back 120extends both vertically and laterally.

Each side frame 112 comprises a front frame tube 122, a rear frame tube124, an upper frame tube or seat tube 126, and a lower frame tube 128.The front frame tube 122 and the rear frame tube 124 are preferablylongitudinally or horizontally spaced and preferably lie in a commonvertical plane. The seat tube 126 and the lower frame tube 128 arepreferably vertically spaced and preferably lie in a common horizontalplane.

The present invention is directed to a foldable link configuration,generally indicated at 129. The link configuration 129 includes aplurality of pivotable links having opposing ends which arecooperatively structured and dimensioned to be pivotally coupled orlinked the to wheelchair side frames 112. The pivotable links arearranged to fold in planes at an angle θ relative to one another. Thelinks are most preferably center-pivoting links that fold innon-parallel planes.

According to one embodiment of the present invention, the links includea foldable seat panel 118 and strut 130. The seat panel 118 and strut130 each preferably have a central hinge, namely, a seat panel hinge 200(shown in FIG. 8) and a strut hinge 172 (shown in hidden line in FIG.5). The seat panel hinge 200 (shown in FIG. 8) is preferably foldableupwardly and a strut hinge 172 (shown in FIG. 5) is preferably foldablein a forward direction to control the folding operation of thewheelchair 110. It should be understood that the hinges 200 and 172could fold in other directions. The strut 130 may fold in a plane, suchas the horizontal plane along the line K in FIG. 1, and the seat panel118 may fold in a plane, such as the vertical plane along the line L inFIG. 1. The angle θ between the planes in which the links fold fromabout 1 to about 90 degrees. The greater the angle θ, the greater theability of the link configuration 129 to withstand lateral deflectionfrom lateral loading. It is preferred that the angle θ between theplanes be greater than 45 degrees, and most preferably, about 90degrees.

A support tube, such as the telescopic tube assembly 132 shown, can bevertically disposed between the seat tube 126 and the lower frame tube128 and preferably lies in a plane common to, or defined by, the frontframe tube 122, the rear frame tube 124, the seat tube 126, and thelower frame tube 128. As is shown in FIG. 2, the telescopic tubeassembly 132 includes an inner tube 134 and an outer sleeve 136. Theinner tube 134 is slidably engageable within an axial bore 138 definedby the outer sleeve 136. An upper end of the outer sleeve 136 can besubstantially perpendicularly attached to a lower surface of the seattube 126. The lower end of the inner tube 134 can be attached to thelower frame tube 128, such as by the tube clamp 140 shown. The upper endof the inner tube 134 can be slidably and axially arranged within theouter sleeve 136.

The tube clamp 140 shown is substantially U-shaped in construction andhas two legs 142 (only one of which is shown). The legs 142 are spacedfrom one another. The inner tube 134 can be received between the legs142. The legs 142 can be sufficiently spaced so as to permit a saddlewasher 144 (shown in hidden line) to fit between the inner tube 134 andeach leg 142 (only one saddle washer 144 is shown).

The inner tube 134, the saddle washers 144, and the legs 142 can beprovided with coaligning holes 146 for receiving a fastener, such as ahex cap screw (not shown). A lock nut (also not shown) may be threadablyengageable with the hex cap screw. The lock nut may be tightenedsufficiently to clamp the lower frame tube 128 and the inner tube 134between the legs 142.

The telescopic tube assembly 132 shown is provided to readilyaccommodate an opposing end of the strut 130 defined by a strut collaror pivot 156, which will be described in greater detail in thedescription that follows. It should be understood that the foregoingtelescopic tube assembly 132 is described for illustrative purposes. Thetelescopic tube assembly 132 is provided to enable the distance betweenthe seat tube 126 and the lower frame tube 128 to be adjusted to permitthe inclination or elevation of the seat tube 126 to be adjusted. Otherarrangements, such as a single support tube (not shown) extendingbetween the seat tube 126 and the lower frame tube 128, may be suitablefor carrying out the invention. It should be understood that the othersupports for pivotally supporting the strut 130 relative to the sideframe 112 may also be suitable for carrying out the invention.

The strut collar or pivot 156 can include an axial bore 157 dimensionedto receive the telescopic tube assembly 132. The strut collar 156 canalso be slidably engageable with the telescopic tube assembly 132 so asto be displaceable along the line A—A. Moreover, the strut collar 156can have an inside diameter that is substantially equivalent to theoutside diameter of the outer sleeve 136. As shown in the drawings, anannular space may be located between the strut collar 156 and the innertube 134 at the lower end 159 of the strut collar 156. A ring 158 can beinserted in this annular space to maintain an axial relationship betweenthe inner tube 134 and the lower end 159 of the strut collar 156.

As shown in FIGS. 3 and 4, the strut 130 may include a plurality ofparts, such as a first part and a second part each defined by acorresponding one of the strut tubes 160 shown. Each strut tube 160 canextend perpendicularly from a strut collar 156. The strut tubes 160 arepreferably rigidly connected to the strut collars 156, such as bywelding the strut collars 156 and the strut tubes 160 together. Astructural web 161 may be rigidly connected between the strut collars156 and the strut tubes 160 to increase the structural integrity of thefoldable strut 130 (shown in side elevation in FIG. 1).

The strut tubes 160 may each have an end 162 provided with an angledabutment surface 168. The abutment surfaces 168 may abut one anotherupon the strut 130. The abutment surfaces 168 may be supported at theends 162 of the strut tubes 160 in any suitable manner. For example, theend 162 of each strut tube 160 may be provided with an opening (shownbut not referenced), thus making the end 162 an open end. The openingmay be dimensioned to receive an end cap 164. More particularly, a plug166 may be an integral part of the end cap 164, and the plug 166 may beinsertable into the opening.

As illustrated in FIG. 4, each end cap 164 may support one of the angledsurfaces 168. The angle α of each angled surface 168 is preferablyequivalent to the angle β between the central axis E of the strut tube160 and a transverse axis T extending through the focal points F of theopposing strut collars 156. The angle α is preferably an angle whichallows substantially unfolding, but prevents the strut tubes 160 fromcompletely unfolding into coaxial alignment with one another, or fromcoaxially aligning with one another.

Each angled surface 168 is preferably provided with a slot 170. Theslots 170 are preferably semi-cylindrical. The semi-cylindrical slots170 preferably extend substantially vertically. The semi-circular slots170 may be transverse with the axis E of the strut tube 160 as shown inFIG. 4. The purpose of the semi-circular slots 170 will become moreapparent in the description that follows.

The strut 130 is preferably adapted to fold in a substantiallyhorizontal plane. This may be accomplished through the aid of a hinge,such as strut hinge 172 shown in hidden line in FIG. 5. The strut hinge172 may be formed by a hub 174 projecting from each end cap 164. Eachhub 174 may have a hole 176. The holes 176 in the hubs 174 preferablycoalign when the hubs 174 are arranged to overlap one another. Thecoaligning holes 176 are preferably dimensioned to receive a hinge pin,such as the hex cap screw 178 shown in FIG. 5. A lock nut 180 may bethreadably engageable with the hex cap screw 178 to hold the hubs 174together to form the strut hinge 172 for pivotally coupling or joiningthe end caps 164, and thus, coupling or joining the ends 162 of thefirst and second strut tubes 160 to permit the strut tubes 160 to foldand unfold relative to one another and thus permit the strut 130 to foldand unfold.

Continuing with reference to FIG. 5, there is an interference member inthe form of a centering and locking assembly 182. The centering andlocking assembly 182 can comprise a swivel bracket 184. The swivelbracket 184 may be provided with a hole 186 through which the hex capscrew 178 holding the hubs 174 together may pass.

As shown in the drawing, the swivel bracket 184 may be arrangedjuxtaposed the upper hub 174. The hole 186 in the swivel bracket 184 maybe arranged to coalign with the coaligning holes 176 in the overlappinghubs 174. With the swivel bracket 184 arranged in this manner, the hexcap screw 178 may be inserted into and through the coaligning holes 176and 186 and the lock nut 180 may be tightened onto the hex cap screw 178to pivotally couple the hubs 174 and the swivel bracket 184 together.

A centering element or device, such as the centering pin 188 shown inhidden line, extends downward from the bottom of the swivel bracket 184.Upon unfolding the foldable strut 130 (shown in FIG. 1), the twoopposing end caps 164 (shown in FIG. 4) converge and thesemi-cylindrical slots 170 cooperatively form a cylindrical bore oropening 190 (shown in FIG. 5 in hidden line). The axis or focal point Pof the centering pin 188 is spaced a predetermined distance from theaxis or focal point H of the strut hinge 172 and is preferably coaxialwith the axis or focal point (also designated as P) of the cylindricalbore 190.

As the foldable strut 130 (shown in FIG. 1) unfolds, the swivel bracket184 is preferably permitted to swivel so as to engage at least one ofthe semi-cylindrical slots 170. The semi-circular slot 170 may thenguide the centering pin 188 to the other semi-circular slot 170. As thefoldable strut 130 completely unfolds, the two end caps 164 (shown inFIG. 4) abut or come into contact with one another and the cylindricalbore 190 is formed by the two semi-circular slots 170. The centering pin188 is captured or trapped in the cylindrical bore 190, which ispreferably horizontally centered along the end cap 164. The cooperativeengagement between the centering pin 188 and the cylindrical bore 190centers the swivel bracket 184 in a substantially fixed positionrelative to the strut 130 or the strut hinge 172. This preferablycenters the swivel bracket 184 in a substantially fixed positionrelative to the seat panel 118 or the seat panel hinge pin 205 (shown inFIG. 8). Most preferably, the swivel bracket 184 is centered laterallysubstantially between the side frames 112.

As shown in FIG. 6, the swivel bracket 184 may include two legs 191 and192 arranged in a substantially L-shaped configuration, thus defining anL-shaped part. A substantially horizontally extending leg 191 may beprovided with the hole 186 through which may pass the hinge pin or hexcap screw 178. As shown in the drawing, an upwardly extending leg 192has an upper edge 193. A fork or slot 194 may originate from the upperedge 193 and extend downward. The slot 194 is preferably engageable withthe seat panel 118 or the seat panel hinge pin 205 (shown in FIG. 8), aswill become more apparent in the description that follows.

As shown in FIGS. 7 and 8, the seat panel 118 may be comprised of twopanel sections 195 and 196 arranged adjacent to one another. Each panelsection 195 and 196 may include opposing ends defined in part by a setof longitudinally spaced collars or pivots 197. Each seat panel collar197 preferably has an axial bore 198 through which a seat tube 126(shown in FIG. 8) may be inserted. It is preferable that two seat panelcollars 197 pivotally couple each panel section 195 and 196 to arespective seat tube 126. The seat panel collars 197 are pivotablerelative to the seat tubes 126 to permit the panel sections 195 and 196to pivot along the lines G—G (shown in FIG. 7) relative to the seattubes 126.

Continuing with reference to FIG. 8, there is illustrated a set oflongitudinally spaced seat panel hinges, generally indicated at 200,formed by a set of hubs 201 and 202 projecting from adjacent ends of thepanel sections 195 and 196 opposite the opposite ends formed in part bythe set of seat panel collars 197. Each hub 201 and 202 preferably has ahole 203 and 204. One set of hubs 201 may coalign with another set ofhubs 202. The holes 203 and 204 (shown in hidden line) in the coaligninghubs 201 and 202 likewise coalign. An elongated seat panel hinge pin 205may be inserted into and through the coaligning holes 203 and 204. Thescat panel hinge pin 205 is preferably provided with a threaded end 206.A lock nut 208 may be engageable with the threaded end 206 of the seatpanel hinge pin 205 to retain the seat panel hinge pin 205 in thecoaligning holes 203 and 204, and thus, form the set of seat panelhinges 200 for pivotally coupling or joining the seat panel sections 195and 196 together.

An opening 210 may be provided between the set of seat panel hinges 200.A portion of the seat panel hinge pin 205 extending through the opening210 may define a handle region 212 of the seat panel hinge pin 205. Thehandle region 212 may be provided or used for lifting the seat panelhinge pin 205 upward, which, in turn, raises the center of the seatpanel 118. That is to say, the panel sections 195 and 196 may bepivotally displaceable along the lines G—G (shown in FIG. 7) by grippingthe handle region 212 of the seat panel hinge pin 205 and lifting theseat panel hinge pin 205 upward along the line Y—Y (shown in FIG. 7). Inaddition to facilitating the folding of the wheelchair 110, the handleregion 212 of the seat panel hinge pin 205 may function as a transporthandle for transporting the wheelchair 110 while in a folded posture.

Now, with reference back to FIG. 9, it is further illustrated that eachseat panel collar 197 may be provided with a cutout 214 adapted toreceive a retainer and guide, such as a saddle washer 216 secured to thebottom of the seat tube 126 within the confines of each cutout 214. Thesaddle washer 216 may be secured with any suitable fastener, such as thePhilips head screw 218 shown in the drawings. The saddle washer 216 mayfunction to retain each seat panel collar 197 in a substantially fixedaxial position along the line D—D relative to the scat tubes 126. Thecutouts 214 and saddle washers 216 may also cooperatively function toguide the seat panel collars 197 throughout the pivotal movement of theseat panel collars 197 along the line G—G (shown in FIG. 7). Theplacement of the seat panel collars 197 on the bottom of the seat tubes126 should not interfere with the pivotal movement of the seat panelcollars 197 and the respective panel sections 195 and 196 along thelines G—G.

The operation of the invention is best understood with reference toFIGS. 10 through 12. As illustrated in FIG. 10, the seat panel 118 mayfold in a plane that is perpendicular to that of the foldable strut 130.It should be understood that the seat panel 118 may fold in planes otherthan a plane perpendicular to that of the foldable strut 130. However,it is preferable that the seat panel 118 fold in a plane that is notparallel to that of the foldable strut 130.

With regard to the embodiment shown in FIG. 10, as the handle region 212(shown in FIG. 8) of the hinge pin 205 (also shown in FIG. 8) is raisedwithin the substantially vertical plane along the line Y—Y, the seatpanel collars 197 may pivot about the seat tubes 126 (shown in FIG. 8).The panel sections 195 and 196 may pivot upward along the lines G—G(shown in FIG. 7).

Throughout the upward movement of the seat panel 118, the collars 156pivot about the telescopic tube assemblies 132 (shown in FIG. 4) alongthe lines B—B (also shown in FIG. 4) and the foldable strut 130 foldsforward in a substantially horizontal plane, generally represented bythe line X. The foldable seat panel 118 and the foldable strut 130 maybe structured and dimensioned to permit the wheelchair 110 to benarrowly folded, and thus, occupy a minimal amount of space when in afolded posture.

The wheelchair 110 (shown in FIG. 1) may be unfolded, for example, bypushing downward on the handle region 212 (shown in FIG. 8) of the seatpanel hinge pin 205 (also shown in FIG. 8) or by merely pulling theopposing side frames 112 (one of which is shown in FIG. 1) apart. As thewheelchair 110 is unfolded, the seat panel collars 197 may again pivotabout the seat tubes 126 (shown in FIG. 8) along the lines G—G (shown inFIG. 7) and the panel sections 195 and 196 may pivot downward, likewisealong the lines G—G. Moreover, the strut collars 156 may pivot about thetelescopic tube assemblies 132 (shown in FIG. 4) along the lines B—B(shown in FIG. 4) and the foldable strut 130 may unfold rearwardly inthe substantially horizontal plane X.

As the wheelchair 110 (shown in FIG. 1) is completely unfolded, thecentering assembly 184 may laterally center the swivel bracket 184 alongthe line C (shown in FIG. 11) substantially between the side frames 112and relative to the seat panel hinge pin 205 (shown in FIG. 8), andthus, relative to the seat panel 118. As described in the descriptionabove, upon unfolding the wheelchair 110, the swivel bracket 184 maypivot so as to permit the centering pin 188 to engage a semi-circularslot 170 (shown in FIGS. 4 and 5) in one of the end caps 164 (also shownin FIGS. 4 and 5). Continued movement of the foldable strut 130 guidesthe centering pin 188 toward the other semi-circular slot 170. As theend caps 164 converge and abut one another, the semi-circular slots 170form a cylindrical bore 190 (as shown in FIG. 5 and as described above)and the centering pin 188 is ultimately captured in the cylindrical bore190, thus centering the swivel bracket 184 along the line C relative tothe seat panel hinge pin 205 (shown in FIG. 8).

Simultaneously, the seat panel hinge pin 205 (shown in FIG. 8) may bedisplaced downward and into engagement with the slot 194 originating atthe upper edge 193 (shown in FIG. 11) of the upwardly extending leg 192of the swivel bracket 184, as shown in FIGS. 11 and 12. The engagementof the seat panel hinge pin 205 with the slot 194 couples the seat panel118 and the foldable strut 130 together.

As shown in FIGS. 5, 6 and 12, the upwardly extending leg 192 of theswivel bracket 184 preferably defines an abutment surface disposed atsome angle ψ (shown in FIG. 12) in the range of about 0 degrees to about90 degrees relative to the horizontally extending leg 191. It is mostpreferable that the angle ψ be about 60 degrees, or that the abutmentsurface defined by the upwardly extending leg 192 be at an angle φ(shown in FIG. 12) of about 30 degrees relative to a vertical axis,indicated along the line V (also shown in FIG. 12), where line V isperpendicular to the horizontally extending leg 191.

Continuing with reference to FIG. 12, the seat panel hinge pin 205(shown in FIG. 11) may be provided with a region, generally indicated at228, which is engageable with the slot 194 originating at the upper edge193 (shown in FIG. 11) of the upwardly extending leg 192. Thisengageable region 228 may have an annular recess defined by a reduceddiameter portion 230. The reduced diameter portion 230 is preferablystructured and dimensioned to fit within the slot 194. The forwardportion or abutment surface 232 of the engageable region 228 ispreferably tapered at an angle that is substantially parallel to theangle φ of the upwardly extending leg 192 relative to the vertical axisV. This parallel relationship insures that adequate surface contactexists between the abutment surface 232 and the upwardly extending leg192. A load on the seat panel 118 or a downward pressure on the seatpanel hinge pin 205 (shown in FIG. 11) may produce tension between theabutment surface 232 of the seat panel hinge pin 205 and the abutmentsurface defined by the upwardly extending leg 192 along the line Y—Y(shown in FIG. 7) to urge the foldable strut 130 (shown in FIG. 1)rearward in the direction of the arrow R against the upwardly extendingleg 192. This resists forward travel of the foldable strut 130, andthus, reduces the risk that the foldable strut 130 will inadvertentlyunfold.

An alternative link configuration 234 is shown in FIGS. 13 and 14. Thislink configuration 234 includes a plurality of pivotable links 236 and238 arranged to travel or fold in planes at an angle λ (shown in FIG.13) relative to one another upon folding or unfolding the wheelchair 110(also shown in FIG. 13). These links may include a foldable upper panel240 and a foldable lower panel 242. The upper and lower panels 240 and242 each preferably have a central hinge, including an upper panel hinge244 (shown in FIG. 14) that is foldable upward and downward and a lowerpanel hinge 246 (also shown in FIG. 14) that is foldable forward andrearward at an upward angle to control the folding operation of thewheelchair. The angle λ of travel of the upper and lower panels 240 and242 shown is preferably about 45 degrees. The upper panel 240 may besubstantially equivalent to the seat panel 118 set forth above. Thelower panel 242 may be substituted in place of the foldable strut, suchas the foldable strut 130 described above. Although not shown, thisembodiment may likewise be provided with a centering and lockingassembly.

It should be clearly understood that the link configurations other thanthose shown and described above may be suitable for carrying out theinstant invention. In accordance with the provisions of the patentstatutes, the principle and mode of operation of this invention havebeen explained and illustrated in its preferred embodiment. However, itmust be understood that this invention may be practiced otherwise thanas specifically explained and illustrated without departing from itsspirit or scope. That is to say, the present invention is not intendedto be limited to the embodiments described above, but encompasses anyand all embodiments within the scope of the following claims.

What is claimed is:
 1. A link configuration for a wheelchair havinglaterally spaced side frames said link configuration comprising: a strutextending between the wheelchair side frames, said strut having opposingends, one of said ends of said strut being pivotally coupled to one ofthe side frames and the other one of said ends of said strut beingpivotally coupled to the other side frame, said strut having a hinge andbeing adapted to fold in a substantially horizontal plane; a seat panelextending between the wheelchair side frames, said seat panel havingopposing ends, one of said ends of said seat panel being pivotallycoupled to one of the side frames and the other one of said ends of saidseat panel being pivotally coupled to the other side frame, said seatpanel having a hinge and being adapted to fold in a substantiallyvertical plane; and an interference member which includes an upwardlyextending fork coupled to said hinge of said strut, said fork beingshaped and dimensioned to receive a portion of said hinge of said seatpanel upon unfolding said seat panel and said strut to couple said hingeof said seat panel and said hinge of said strut together.
 2. The linkconfiguration of claim 1, wherein said strut includes a first part and asecond part pivotally coupled together by said hinge, said first andsecond parts each having an abutment surface, said abutment surface ofsaid first and second parts abutting one another upon unfolding saidstrut to prevent said first and second parts from co-axially aligningwith one another.
 3. The link configuration of claim 1, furthercomprising a centering pin coupled to said fork and extendingsubstantially vertically downward, said strut being adapted to form anopening to capture said centering pin upon unfolding said seat panel andsaid strut to couple said fork to said hinge of said seat panel.
 4. Thelink configuration of claim 3, wherein said strut includes a first partand a second part pivotally coupled together by said hinge of saidstrut, said first and second parts having an abutment surface, saidabutment surface of said first and second parts abutting one anotherupon unfolding said strut, said abutment surfaces each comprise asubstantially vertically extending, substantially semi-cylindrical slot,said centering pin being substantially cylindrical and extendingsubstantially vertically downward from said fork, said slot in saidabutment surface of said first part being adapted to coaxially alignwith said s lot in said abutment surface of said second part uponabutment of said abutment surfaces to form a substantially cylindricalbore for receiving said centering pin to center said fork relative tosaid strut.
 5. A link configuration for a wheelchair having laterallyspaced side frames, said link configuration comprising: a strutextending between the wheelchair side frames, said strut having opposingends, one of said ends of said strut being pivotally coupled to one ofthe side frames and the other one of said ends of said strut beingpivotally coupled to the other side frame, said strut having a hinge andbeing adapted to fold in a substantially horizontal plane; a seat panelextending between the wheelchair side frames, said seat panel linkhaving opposing ends, one of said ends of said seat panel beingpivotally coupled to one of the side frames and the other one of saidends of said seat panel being pivotally coupled to the other side frame,said seat panel having a hinge and being adapted to fold in asubstantially vertical plane, said scat panel hinge comprising a hingepin having an outer surface, a reduced diameter portion, and an abutmentsurface between said outer surface and said reduced diameter portion;and an interference member coupled to said strut hinge and engageablewith said seat panel hinge upon unfolding said strut and said seat panelto couple said strut and said seat panel together, said interferencemember including a substantially L-shaped part having a substantiallyhorizontally extending leg and a upwardly extending leg, said L-shapedpart being pivotally coupled to said strut hinge by a strut hinge pin,said upwardly extending leg defining a fork, said fork being shaped anddimensioned to receive said reduced diameter portion of said seat panelhinge pin, said upwardly extending leg having an abutment surfaceadapted to engage said abutment surface of said seat panel hinge pinupon unfolding said seat panel and said strut and to produce tensionbetween said abutment surface of said upwardly extending leg and saidabutment surface of said seat panel hinge pin upon applying a load tosaid seat panel.
 6. The link configuration of claim 5, furthercomprising a substantially cylindrical centering pin extendingsubstantially vertically downward from said substantially horizontallyextending leg, said strut including a first part and a second partpivotally coupled together by said hinge of said strut, said first andsecond parts each having an abutment surface, said abutment surface ofsaid first and second parts abutting one another upon unfolding saidfirst and second parts, said abutment surface of said first and secondparts each comprise a substantially vertically extending, substantiallysemi-cylindrical slot, said slot in said abutment surface of said firstpart being adapted to align coaxially with said slot in said abutmentsurface of said second part upon abutment of said abutment surfaces insaid first and second parts to form a cylindrical opening for receivingsaid centering pin to center said fork relative to said strut.
 7. Thelink configuration of claim 5, further comprising a centering elementcoupled to said interference member and engageable with said strut forsubstantially centering said interference member relative to said strutand said seat panel.
 8. The link configuration of claim 5, where in saidabutment surface of panel hinge pin is disposed at an angle in a rangeof about 40 degrees to about 90 degrees relative to a horizontal axisthrough said seat panel hinge pin, and said upwardly extending leg ofsaid L-shaped part is disposed at an angle in a range of about 40degrees to 90 degrees relative to said substantially horizontallyextending leg.
 9. In combination: a wheelchair having laterally spacedside frames; a strut extending between the wheelchair side frames, saidstrut having opposing ends, one of said ends of said strut beingpivotally coupled to one of said side frames and the other one of saidends of said strut being pivotally coupled to the other one of said sideframes, said strut having a hinge formed in part by a hinge pin, saidstrut being adapted to fold in a substantially horizontal plane; a seatpanel extending between the wheelchair side frames, said seat panelhaving opposing ends, one of said ends of said seat panel beingpivotally coupled to one of said side frames and the other one of saidends of said seat panel being pivotally coupled to the other one of saidside frames, said seat panel having a hinge formed in part by a hingepin, said seat panel being adapted to fold in a substantially verticalplane; an upwardly extending fork coupled to said strut hinge and beingshaped and dimensioned to receive a portion of said seat panel hingeupon unfolding said strut and said seat panel to couple said hinge ofsaid seat panel and said hinge of said strut together; and aninterference member coupled to said fork and engageable with said strutupon unfolding said strut to center said fork relative to said strut.10. The link configuration of claim 9, wherein said interference memberincludes a centering pin coupled to said fork and extendingsubstantially vertically downward, said strut being adapted to form anopening to trap said centering pin upon unfolding said seat panel andsaid strut to center said fork relative to said seat panel and saidstrut.
 11. A link configuration for a wheelchair having laterally spacedside frames, said link configuration comprising: a foldable strutextending substantially between the wheelchair side frames, said struthaving opposing ends, one of said ends being pivotally coupled to one ofthe side frames and the other one of said ends being pivotally coupledto the other side frame, said strut further having a strut hinge formedin part by a strut hinge pin, said strut being foldable in asubstantially horizontal plane; a foldable seat panel extending betweenthe wheelchair side frames, said seat panel having opposing ends, one ofsaid ends of said seat panel being pivotally coupled to one of the sideframes and the other one of said ends of said seat panel being pivotallycoupled to the other side frame, said seat panel having a seat panelhinge formed in part by a seat panel hinge pin, said seat panel beingfoldable in a substantially vertical plane; an upwardly extending forkcoupled to said strut hinge, said fork being shaped and dimensioned toreceive a portion of said seat panel hinge upon unfolding said seatpanel and said strut to couple said seat panel hinge pin and said struthinge pin together; and a centering pin coupled to said fork andextending substantially vertically downward, said strut being adapted toform a substantially cylindrical opening to capture said centering pinupon unfolding said seat panel and said strut to laterally center saidfork relative to said strut.
 12. The link configuration of claim 11,wherein said strut includes a first part and a second part each having afirst end and a second end, said first end of each one of said first andsecond parts being pivotally coupled to a corresponding one of the sideframes, said second end of said first and second parts being pivotallycoupled together by said strut hinge, said second end of said first andsecond parts each having an abutment surface, said abutment surface ofsaid first and second parts abutting one another upon unfolding saidstrut to prevent said first and second parts from aligning coaxiallywith one another.
 13. The link configuration of claim 11, furthercomprising a substantially L-shaped part having a substantiallyhorizontally extending leg and a upwardly extending leg, said L-shapedpart being pivotally coupled to said strut hinge by said strut hingepin, said fork being defined by said upwardly extending leg, said seatpanel hinge pin comprising an outer surface, a reduced diameter portion,and an abutment surface between said outer surface and said reduceddiameter portion, said fork being shaped and dimensioned to receive saidreduced diameter portion of said seat panel hinge pin, said upwardlyextending leg having an abutment surface adapted to engage said abutmentsurface of said seat panel hinge pin upon unfolding said seat panel andsaid strut and to produce tension between said abutment surface of saidseat panel hinge pin and said abutment surface of said upwardlyextending leg upon applying a load to said seat panel.
 14. The linkconfiguration of claim 13, wherein said strut includes a first part anda second part pivotally coupled together by said strut hinge, said firstand second parts each having an abutment surface, said abutment surfacesof said first and second parts abutting one another upon unfolding saidstrut, said abutment surfaces of said first and second parts eachcomprise a substantially vertically extending, substantiallysemi-cylindrical slot, said centering pin being substantiallycylindrical and extending substantially vertically downward from saidsubstantially horizontally extending leg, said slot in said abutmentsurface of said first part being adapted to coaxially align with saidslot in said abutment surface of said second part upon abutment of saidabutment surfaces of said first and second parts to form a cylindricalopening for receiving said centering pin to laterally center said forkrelative to said strut.
 15. The link configuration of claim 13, whereinsaid abutment surface of said seat panel hinge pin is disposed at anangle in a range of about 0 to about 60 degrees relative to a horizontalaxis through said seat panel hinge, and said abutment surface of saidupwardly extending leg is disposed at an angle in a range of about 0 to60 degrees relative to said substantially horizontally extending leg.16. In combination: a wheelchair having laterally spaced side frames;and a link configuration comprising: a foldable strut extending betweensaid wheelchair side frames, said strut having opposing ends, one ofsaid ends being pivotally coupled to one of said side frames and theother one of said ends being pivotally coupled to the other one of saidside frames, said strut further having a strut hinge formed in part by astrut hinge pin, said strut being foldable in a substantially horizontalplane; a foldable seat panel extending between said wheelchair sideframes, said seat panel having opposing ends, one of said ends of saidseat panel being pivotally coupled to one of said side frames and theother one of said ends of said seat panel being pivotally coupled to theother one of said side frames, said seat panel having a seat panel hingeformed in part by a seat panel hinge pin, said seat panel being foldablein a substantially vertical plane; an upwardly extending fork coupled tosaid strut hinge, said fork being shaped and dimensioned to receive aportion of said seat panel hinge upon unfolding said seat panel and saidstrut to couple said seat panel and said strut together; and a centeringpin coupled to said fork and extending substantially verticallydownward, said strut being adapted to form a cylindrical slot to capturesaid centering pin upon unfolding said seat panel and said strut.